The invention relates to interruption devices located on explosion trains for safety purposes. Safety devices are found in numerous equipments comprising a warhead and their role is to increase safety during storage, handling and transport.
Such safety devices in general comprise a part movable between a position in which it restrains an activation process and a position in which it allows or causes it. Most safety devices have the drawback of comprising a movable part and a mechanism for moving it. Safety devices including a fusible material have also been suggested. For instance, U.S. Pat. No. 2,453,151 (Miller) discloses a safety device for a rotatable projectile, comprising a barrier of an alloy which is fused by heat on discharge of the projectile from a gun for permitting operation of the striker. However, that device relies on centrifugal force for arming the train. Similarly, British No. 453,685 (Remondy) discloses a fuze whose striker is retained by a fusible joint until the latter has been heated by combustion of a slow burning composition. There is also known an ejectable fuze carried by a warhead with a connection by a joint which fails at a predetermined level of temperature for lessening the chances of the warhead exploding in a fire situation (U.S. Pat. No. 4,022,130 to Johnson et al.). Reliance is had on the pressure from deterioration of the booster material for ejection.
It is an object of the invention to provide an explosion train interruption device comprising no moving part and not requiring assistance by centrifugal force. It is a more specific object to provide such a device for activating (or de-activating) an explosion train should there be a rise in the surrounding temperature beyond a predetermined value, relying on an eutectic alloy part melting at said temperature and placed in the train. It is still a more specific object to provide an activation device for use in a system for venting a propulsion charge of an ordnance item carrying a warhead upon temperature increase beyond a predetermined value.
According to an aspect of the invention, there is provided an activation device comprising a casing, primer means of a venting system in said casing, a striker slidably received in said casing for movement toward said primer means, spring means for urging said striker toward said primer means, and retaining means cooperating with said striker for positively retaining said striker at a distance from said primer means and including an eutectic material selected to melt at a predetermined temperature lower than a temperature of ignition.
For ensuring the storage safety of an ordnance item having a propellent charge and a warhead, the eutectic alloy retaining means may form or hold a restraining bolt of a striker against the action of a spring tending to project this striker onto an activation primer of a deconfinement system for the propellent charge; thus, should a fire occur in the storage premises, the risk of seeing the propellent charge project the military charge up to great distances is overcome. The eutectic forming the part will then be chosen from a material which loses its cohesion above the maximum anticipated storage temperature, which is usually 70.degree. C. A second eutectic part may be interposed between the striker and the primer, or in the explosion train properly speaking. In this case, it will be made from a material having a melting point less than that of the first part.
In another embodiment, an eutectic alloy part is placed between two elements in the explosion train so as to stop propagation of the detonation wave until the eutectic has been brought into liquid condition, by heating possibly caused by means of an electric resistance buried in the part or surrounding it. The thickness of the part will be very different depending on the energy to be absorbed: the thickness may be reduced when the part is placed between a primer and relay; it will in general need to be of a thickness substantially greater when the part is between a relay and detonator.